The shipment of dry bulk powder materials in, for example, railroad hopper cars results in settling or compacting of the materials. When dry bulk materials such as pigments arrive at a users plant various methods have been proposed for moving the pigment from the railroad hopper car to storage facility for subsequent use.
In U.S. Pat. No. 3,512,842 owned by the assignee of this invention, it was proposed to introduce warm water into the dry bulk powder to form a slurry. The particles would then wet out after a soaking period of several hours. Air was subsequently injected into the slurry to facilitate the formation of a homogeneous slurry which would be suitable for pumping. Air was introduced through pipes mounted along the sides and bottom of the hopper with multiple holes, mutually spaced, for expelling air under pressure. Typically the pipes were one half inch in diameter with 3/16 inch holes spaced about one foot apart and air pressure of 80 to 100 pounds per square inch (gauge) was used.
Water at a temperature of between 73.degree. F. and 100.degree. F. was introduced at the bottom of the hopper at a low controlled rate to make up a slurry containing about 2.3 to 2.4 pounds of sodium alumino silicate per gallon.
The patent further states that after air agitation, the slurry is recycled by pumping the slurry from the bottom of the hopper car and returning it to the top to further assist in forming a homogeneous slurry. The slurry then can be pumped to a storage tank for use later in the plant.
This procedure requires high capacity pumps. While at rest, the slurry material often became a jelly-like material requiring further agitation to become fluid. In addition, a concentration in excess of about 2.4 pounds per gallon has such a high viscosity that pumping was difficult.
Subsequently, in U.S. Pat. No. 4,036,663, also assigned to the assignee of this invention, an alternate procedure was proposed wherein a finely divided deliquescent salt was admixed with the dry powder before water was admitted. The salt was typically blended in a weight range of about 0.1% to 3% by weight of the pigment mixture before slurrying. While this procedure was effective, it increased the cost of the pigment and required a facility for the dry mixing step.
A further effort to improve the off loading of dry powder is described in U.S. Pat. No. 4,189,262. In that patent a plurality of aeration devices are mounted in the bottom of the hopper. The aeration devices were as disclosed in U.S. Pat. No. 3,929,261 and included a head with a movable flap which fluttered as air passed through the head and into the surrounding powder material of the hopper compartment.